Low temperature curing polyuretdione compositions
View Patent ↗Composition and process for low temperature curing of polyuretdione-polyol compositions in which the polyuretdione is prepared from a polyisocyanate with isocyanate groups and a polyol containing primary hydroxyl groups. The catalyst for the composition and process is an amine catalyst containing the group —N═C—N—, being aprotic, having a pKa greater than 20 and upon addition to the liquid coating composition causing a phase-change of the coating composition from liquid to solid at 25° C. and 1 atm. within one week.
1. A liquid coating composition that cures at 20-70° C. comprising:
a) a polyuretdione prepared from a polyisocyanate,
b) a polyol, and
c) an amine catalyst,
wherein the catalyst contains the group
is aprotic, has a pKa greater than 20 and upon addition to the liquid coating composition causes a phase-change of the coating composition from liquid to solid at 25° C. and 1 atm. within one week.
2. The composition of claim 1 wherein
a) is present in amounts of 10 to 90% by weight, and
b) is present in amounts of 10 to 90% by weight;
the % by weight being based on total weight of a) and b).
3. The composition of claim 1 wherein the amine catalyst is present in amounts of 0.05 to 5% by weight.
4. The composition of claim 1 , wherein the amine catalyst has a structure according to formula I:
wherein R 1 represents linear or branched alkyl, preferably t-butyl, or in combination with R 4 , is a connecting segment selected from the group consisting of N═CH and
R 2 represents H, linear or branched alkyl, preferably methyl, dimethylamine, or in combination with R 3 is a connecting segment selected from the group consisting of
R 3 represents Na, linear or branched alkyl, preferably methyl, or in combination with R 2 , is a connecting segment selected from the group consisting of and
R 4 represents linear or branched alkyl, preferably methyl, or in combination with R 1 , is a connecting segment selected from the group consisting of N═CH and
and
and wherein R 1 and R 4 may together form an N-heterocyclic ring, and R 2 and R 3 may together form an N-heterocyclic ring.
5. The composition of claim 1 wherein the amine catalyst is selected from the group consisting of 1,8-diazabicyclo[5.4.0]undec-7ene, 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,4,5,6-tetrahydro-1,2-dimethylpyrimidine, 1,2,4-triazole, sodium derivative and 2-tert-butyl-1,1,3,3-tetramethylguanidine.
6. The composition of claim 1 wherein the polyuretdione is prepared by reaction of a uretdione group containing polyisocyanate with at least one polyol an optionally a blocking agent for isocyanate.
7. The composition of claim 1 wherein the polyuretdione contains from 5 to 45% by weight of uretdione groups; 10 to 55% by weight urethane groups and less than 2% by weight free isocyanate groups the percentage by weight being based in total weight of resin containing uretdione, urethane, and/or isocyanate groups.
8. The composition of claim 1 wherein the polyisocyanate contains from 4 to 20 carbon atoms.
9. The composition of claim 7 wherein the polyisocyanate is a (cyclo)aliphatic polyisocyanate.
10. The composition of claim 1 wherein the polyisocyanate is a diisocyanate.
11. The composition in claim 1 wherein the polyisocyanate is selected from the group consisting of 1,6-hexamethylene diisocyanate, isophorone diisocyanate and mixtures thereof.
12. The composition of claim 1 , wherein the polyuretdione contains one or more groups consisting of isocyanurate, biuret, and iminooxadiazine dione groups.
13. The composition of claim 1 wherein the polyol is a polymeric polyol having a hydroxyl value of 10 to 180.
14. The composition of claim 13 wherein the polymeric polyol is selected from a polyether polyol, a polyester polyol, a polyurethane polyol, a hydroxy-group-containing (meth)acrylic polymer and a polycarbonate polyol.